The field of the invention is an apparatus for converting olefins mixed with paraffins into higher molecular weight compounds for easier separation from unconverted paraffins.
Fluid catalytic cracking (FCC) is a catalytic hydrocarbon conversion process accomplished by contacting heavier hydrocarbons in a fluidized reaction zone with a catalytic particulate material. The reaction in catalytic cracking, as opposed to hydrocracking, is carried out in the absence of substantial added hydrogen or the consumption of hydrogen. As the cracking reaction proceeds substantial amounts of highly carbonaceous material referred to as coke are deposited on the catalyst to provide coked or spent catalyst. Vaporous lighter products are separated from spent catalyst in a reactor vessel. Spent catalyst may be subjected to stripping by an inert gas such as steam to strip entrained hydrocarbonaceous gases from the spent catalyst. A high temperature regeneration with oxygen within a regeneration zone burns coke from the spent catalyst which may have been stripped. Various products may be produced from such a process, including a gasoline product and/or light product such as propylene and/or ethylene.
In such processes, a single reactor or a dual reactor can be utilized. Although additional capital costs may be incurred by using a dual reactor apparatus, one of the reactors can be operated to tailor conditions for maximizing products, such as light olefins including propylene and/or ethylene.
It can often be advantageous to maximize yield of a product in one of the reactors. Additionally, there may be a desire to maximize the production of a product from one reactor that can be recycled back to the other reactor to produce a desired product, such as propylene.
The cracking of C4-C7 olefins produces a high yield of propylene. The recycle of a C4-C7-rich stream back to an FCC reactor can be used to further increase propylene production. This recycle, however, leads to a concentration of the more refractory paraffins in the recycle stream and requires either a significant purge or a large recycle flow rate. There is no simple way of separating the olefins from the paraffins for a stream with such a wide range of boiling points.
The oligomerization of olefins over heterogeneous catalyst to heavier olefins for making motor fuels is a known technology. It is also known to alkylate olefins with paraffins over homogeneous acid catalyst to make motor fuels. Alkylation of olefins with benzene and other aromatic components typically over heterogeneous catalyst is also known for making petrochemical stock including detergent precursors.
There is need for easily separating olefins from paraffins in product streams.